Ahmed Mohamed Mahmoud Ibrahim

Tribological Behavior of NiAl–1.5 wt% Graphene Composite Under Different Velocities

The progress in aerospace field requires a new NiAl matrix composite that can stand against wear and decrease the energy dissipation through decreasing friction. In this study, the tribological behavior of NiAl–1.5 wt% graphene composite is investigated at room temperature under a constant load of 12 N and different sliding velocities. The results show that the friction coefficient and wear rate increase with increasing sliding velocity from 0.2 to 0.4 m/s due to the adhesion between the sliding bodies and tearing of the graphene layer. The friction coefficient and wear rate tend to decrease at a sliding velocity of 0.6 m/s as a result of severe plastic deformation and grain refinement of the worn surface. However, at 0.8 m/s the friction coefficient reaches a minimum value and the wear rate increases and changes the wear mechanism to fatigue wear. It can be concluded that various wear mechanisms lead to different tribological performance of NiAl–1.5 wt% graphene composite.

Tribological behavior of a TiAl matrix composite containing 10 wt% Ag investigated at four wear stages

The useful longevity of mechanical components, such as gears and sliding bearings, were related with their tribological behaviors. The tribological behavior of a TiAl matrix composite containing 10 wt% Ag (TiAl–10 wt% Ag) was investigated at the four different wear stages. Wear stages, which were identified by the obtained friction coefficient and wear rate, were divided into the initial wear stage (INITIAL), fast wear stage (FAST), stable wear stage (STABLE) and severe wear stage (SEVERE). The results showed that tribological behavior at INITIAL was improved for work hardening. The friction coefficient and wear rate at FAST were small for the formation of mixed layers containing a solid lubricant Ag. Excellent tribological behavior at STABLE was attributed to the existence of lubricant films containing massive amounts of solid lubricant Ag. Poor tribological behavior of TiAl–10 wt% Ag at SEVERE was obtained for the lubricant film destroyed by the propagation of fatigue cracks. It was found that TiAl–10 wt% Ag, because of the excellent tribological behavior at STABLE, could be chosen as a promising structural material for mechanical components.

Formation of Friction Layers in Graphene-Reinforced TiAl Matrix Self-Lubricating Composites

The friction layer structure has been proved to be formed during severe plastic deformation and markedly improves the tribological properties of material. The dry friction and wear performance of graphene-reinforced TiAl matrix self-lubricating composites (GTMSC) at different sliding velocities are systematically researched. GTMSC show the best tribological properties and special friction layer structure containing a wear-induced layer and a grain refinement layer with a nanocrystalline (NC) structure under surface after sliding at a sliding speed of 1.1 m/s. Nanoindentation results show that the grain refinement layer has a higher hardness and elastic modulus than the wear-induced layer. This special microstructure of friction layers beneath the surface after sliding leads to a low coefficient of friction and high wear resistance of GTMSC. Moreover, it is deduced that the appearance of an NC structure results in hardening of the material. The formation mechanisms of friction layers are researched in detail. It can be concluded that the formation of a wear-induced layer results from frictional heat and fracture of the counterpart. The formation of a grain refinement layer is due to severe plastic deformation and dynamic recrystallization. Severe plastic deformation results in the formation of an NC structure and dynamic recrystallization leads to grain refinement.

Synergetic Lubricating Effect of WS2 and Ti3SiC2 on Tribological Properties of Ni3Al Matrix Composites at Elevated Temperatures

The tribological behaviors of the Ni3Al-WS2-Ti3SiC2 composites and synergistic effect of composite solid lubricants are investigated from room temperature to 800°C. The results show that the Ni3Al matrix composites (NASC) exhibit excellent tribological properties throughout the test temperatures compared to Ni3Al-based alloy. The excellent tribological properties of NASC are attributed to the synergistic lubricating effect of WS2 and Ti3SiC2. A lubricating film could be formed below 400°C, and an oxidation protection film is formed above 400°C on the worn surface of NASC during the sliding process, leading to low coefficients of friction (0.18–0.39) and wear rates (1.5–3.7 × 10−5 mm3N−1m−1).

Tribological Characteristics of NiAl Matrix Composites with 1.5 wt% Graphene at Elevated Temperatures: An Experimental and Theoretical Study

In this study, the tribological properties of NiAl matrix composites with 1.5 wt% graphene nanoplatelets (NAG) at elevated temperatures were simulated and tested. NAG exhibits excellent characteristics at 100 and 200°C due to the formation of metal oxides and graphene nanoplatelets lubrication film. Furthermore, the removed layer thickness, the stress distributions, and the high stresses of the affected layer have been estimated theoretically. At 400°C, the friction coefficient increased due to the absence of the lubrication layer. In addition, the wear rate increased due to the excessive stresses, the increased layer thickness removal, and the propagation of subsurface cracks.

Tribological Performance of Ni3Al Self-Lubricating Composites with Different Content of TiC at Elevated Temperature

Ni3Al-MoS2-TiC composites (NMTC) were fabricated using spark plasma sintering. The effect of TiC content on tribological properties and antiwear mechanisms of NMTC at high temperatures was investigated. The results showed that NMTC containing 10 wt% MoS2 and 6 wt% TiC exhibited the excellent tribological properties from 25 to 600°C. At 400°C, NMTC had the lowest friction coefficient of 0.28 and the considerable lower wear rate of 3.02 × 10−5 mm3 N−1 m−1. The excellent tribological properties of NMTC were attributed to the synergetic action of the lubricant-phase MoS2 and reinforcing-phase TiC.

Wear rate of a TiAl matrix composite containing 10 wt% Ag predicted using the Newton interpolation method

The longevity of a mechanical component was evaluated by predicting the wear rate of the material. The primary purpose of this study was to construct three prediction formulas (W4(F), W4(n) and W4(t)) to predict the wear rate at different applied loads F, rotation speeds n and sliding times t based on a TiAl matrix composite containing 10 wt% Ag. Prediction formulas of wear rate, which were constructed by the Newton interpolation method, were evaluated by making a comparison between the testing error and computational error. The results showed that the prediction formulas (W4(F), W4(n) and W4(t)) of wear rate were accepted for smaller computational errors. It was found that the prediction accuracy gradually increased for the higher binding force of wear debris at larger applied loads F (see formula W4(F)), and slightly decreased for random impacting of wear debris at higher rotation speeds n (see formula W4(n)), as well as being relatively stabilized for incessant forming of anti-friction films at different sliding times t (see formula W4(t)).

Research on the Thickness of the Friction Layer of Ni 3 Al Matrix Composites with Graphene Nanoplatelets

Dry sliding tribological tests of Ni3Al matrix composites (NMCs) with/without graphene nanoplatelets (GNPs) under different working conditions are undertaken in this article. The results show that GNPs in NMCs make a major contribution to the formation of the friction layer, which is responsible for the reduction of the friction coefficient and improvement of wear resistance. In addition, with the increase in the sliding velocity and normal load, the friction coefficient decreases to a stable value and the wear rate increases to a stable value. This article also examines the possibility of describing the formation of the friction layer during the sliding process. The formation of the friction layer can be divided into two processes: the formation of the fine grain layer and the material loss of the surface layer. The strain rate intensity factor is used to describe the formation of the fine grain layer, and the functional relation of the material loss of the surface layer is obtained by the experimental data. As a result, a specific formula for calculating the thickness of the friction layer of NMCs with GNPs is found.

Improving the tribological properties of NiAl matrix composites via hybrid lubricants of silver and graphene nano platelets

This work presents a comprehensive study of the synergistic tribological effect of combined solid lubricants of silver and graphene nano platelets (GNPs). Moreover, it presents a comparative study of the tribological characteristics of NiAl (NA), NiAl-10 wt% silver (NAS), NiAl-1.5 wt% GNPs (NAG), NiAl-1.5 wt% GNPs-10 wt% silver (NAGS10) and NiAl-1.5 wt% GNPs-15 wt% silver (NAGS15) composites based on tribological and microstructural tests. The NAGS10 composite shows the lowest friction coefficients and the highest wear resistance among the whole composites at different sliding velocities and applied loads, while NA exhibits the highest friction coefficients and wear rates at the same sliding conditions. The microstructural tests of NAGS10 and NAGS15 composites reveal the formation of GNPs and silver enriched islands which act as the bearing areas and play the major role in loading transition. Furthermore, those islands ease the slipping of the graphene layers over the NiAl substrate.

Effect of Hardness Ratio on the Wear Performance and Subsurface Evolution of Ni3Al Matrix Composites

ABSTRACT A favorable hardness ratio (Hdisk/Hpin = Hd/Hp) could lead to a transition to mild wear during sliding contact. To determine a more appropriate Hd/Hp value for the sliding wear, the dry sliding pin-on-disk wear tests of Ni3Al matrix composites (NMCs) with multilayer graphene (MLG) are undertaken at Hd/Hp values of 0.99, 0.83, 0.42, and 0.35 at sliding speeds of 0.1, 0.3, 0.5, and 0.7 m/s. It is found that the tribological properties of NMCs are strongly affected by the various hardness ratios. At 0.1 m/s, the friction coefficient decreases with a decrease in Hd/Hp value. The low friction coefficient is 0.14 and the wear rate is 0.9 × 10−5 mm3 N−1m−1 under the ceramic counterpart with Hd/Hp of 0.35. At 0.7 m/s, the tribological properties show the opposite trend with a decrease in Hd/Hp. At an Hd/Hp of 0.35, the smooth compact layer on the worn surface could decrease the friction at 0.1 m/s, and the improved hardness in the subsurface by strain hardening would play an important role in the improvement of wear resistance. Under the metal counterpart with Hd/Hp of 0.99, plastic deformation only occurs on the contact surface and the MLG could suppress further shear deformation in the subsurface, leading to a low wear rate (2.4 × 10−5 mm3 N−1m−1) and friction coefficient (0.15) at 0.7 m/s.